1. Heat oven to 425 degrees F.
2. In a small bowl, whisk together vinegar, mustard, paprika, 1/4 tsp of the salt and 1/8 tsp of the pepper. While whisking, add oil in a stream.
3. Toss potatoes with 2 tbsp of the dressing and spread onto a rimmed baking sheet. Sprinkle paprika on cut side of onion and add to pan, cut side up. Roast at 425 degrees for 20 minutes.
4. Stir potatoes and push to one side of the pan. Remove onion to a cutting board. Toss asparagus with 1 tbsp of the remaining dressing and add to pan. Continue to roast at 425 degrees for 20 minutes.
5. Meanwhile, toss salmon with remaining 2 tbsp dressing. Cut onion into 4 wedges, then cut wedges in half. Thread eight 6- to 8-inch skewers with salmon, onion and cherry tomatoes. Season with 1/4 tsp salt and 1/8 tsp pepper.
6. Remove potatoes and asparagus from oven. Season with remaining 1/4 tsp salt and 1/4 tsp pepper. Turn oven temperature up to broil.
7. Broil skewers, 4 inches from heat, for 5 minutes, turning once. Serve skewers over roasted vegetables.